Technical Abstract:
Respiratory epithelial cells are the first cells which are infected with influenza virus and these cells play a major role in influenza pathogenesis. However, many studies have shown that alveolar macrophages also play a very important role in the pathogenesis and immunity to influenza infection. Until recently, useful porcine macrophage cell lines were not available for viral/influenza studies. Recently two monocyte-derived porcine macrophage cell lines (Cdelta2+ and Cdelta2-) have been developed and characterized for their phagocytic ability and biochemical properties. We further characterized these two cell lines for the presence of sialic acid based cell surface receptors responsible for the influenza virus infection. Both Cdelta2+ and Cdelta2- cells mainly expressed sialic acid receptor Sial-2,6-Gal as determined by SNA lectin binding using flow cytometry. The next step was to check if influenza viruses (swine H1N1/A/SW/IOWA and human B/FLORIDA/4/2006 strains) were able to infect and replicate in these cells. Using immunoflourescence assays, we were able to show that these viral strains infected both cell lines. We also determined the percentage of Cdelta2+ and Cdelta2- cells which were infected by both of these viruses using flow cytometry. We were also able to show, using hemagglutination (HA) assays, that both influenza A and B viruses were able to replicate in both Cdelta2+ and Cdelta2- cells. We further infected Cdelta2+ cells with these two influenza viruses and studied the changes in gene expression of different pathogen-recognition receptors (PRRs), cytokines, chemokines and anti-microbial peptides. Both swine influenza A virus and human influenza B virus strains induced significant changes in various toll-like receptors (TLRs), RIG1-like receptors (RLRs), type 1 interferons, pro-inflammatory cytokines and chemokines gene expression. Overall, we showed that both Cdelta2+ and Cdelta2- cell lines are susceptible to influenza infection and can be successfully used to study the pathogenesis of swine influenza viruses.